1. Field of the Invention
The present invention relates to a refrigerating apparatus.
2. Description of the Related Art
As a refrigerating apparatus configured to cool an inside of a low-temperature storage which stores storage objects such as refrigerated articles, for example, a dual refrigerating apparatus is known. The dual refrigerating apparatus includes a high-temperature side refrigerant circuit in which a first refrigerant is sealed and a low-temperature side refrigerant circuit in which a second refrigerant whose boiling point is lower than that of the first refrigerant is sealed. Also, an evaporator of the high-temperature side refrigerant circuit (hereinafter referred to as a high-temperature side evaporator) and a condenser of the low-temperature side refrigerant circuit (hereinafter referred to as a low-temperature side condenser) form a cascade condenser so as to mutually exchange heat. As a result, the second refrigerant is condensed by a cooling effect of the high-temperature side refrigerant circuit and the inside of the storage is cooled by the cooling effect of the low-temperature side refrigerant circuit. A cooling temperature inside the storage is detected by a sensor. In accordance with the detected cooling temperature of the inside of the storage, rotation speeds of a compressor of the high-temperature side refrigerant circuit (hereinafter referred to as a high-temperature side compressor) and a compressor of the low-temperature side refrigerant circuit (hereinafter referred to as a low-temperature side compressor) are controlled, respectively, and the inside of the storage is brought to a target cooling temperature (e.g., see Japanese Patent Laid-Open No. 5-142294).
In a case where control is made in such a manner that the cooling temperature inside the storage becomes constant, a temperature of the cascade condenser is preferably at a constant temperature. However, if specifications of the high-temperature side compressor and the low-temperature side compressor are different or their performances vary even if the specifications are the same, despite the fact that operations of the both compressors are simultaneously controlled by a detection output of the sensor, timings at which an evaporation temperature of the high-temperature side evaporator and a condensation temperature of the low-temperature side condenser are changed might not match, or rates of the change of the evaporation temperature of the high-temperature side evaporator and the condensation temperature of the low-temperature side condenser might be biased more than necessary. In this case, if the cooling temperature inside the storage changes, there was a possibility that time required until the temperature of the cascade condenser comes to a constant temperature becomes longer and the time until the cooling temperature in the storage comes to the constant temperature becomes longer.